Ok, I am so not an Exchange dude but here goes;
I've installed Exchange 2010 hub transport, client access, & mailbox roles on member server in coexistence with Exchange 2003. Exchange 2010 test mailboxes can send & receive mail from Exchange 2010 mailboxes (from local MDB) and can send mail to Exchange 2003 mailboxes and to mailboxes outside over internet, BUT Exchange 2010 mailboxes cannot receive mail from my Exchange 2003 mailboxes nor from mailboxes outside over internet. This sounds like a connector problem to me, but I cannot figure out what the dealio is. Any and all help would be ginormously appreciated.